Osmium Oxysulphide, Os₂O₃(SH)₂

Osmium Oxysulphide, Os₂O₃(SH)₂, is obtained as a brown powder by the action of hydrogen sulphide on dry osmic acid, H₂OsO₄. The reaction is very vigorous, the mass being raised to glowing temperature, water and sulphur vapour being emitted:

2H₂OsO₄ + 4H₂S = Os₂O₃(SH)₂ + 5H₂O + 2S.

The oxysulphide dissolves in acids evolving hydrogen sulphide.

The heat of the reaction indicates that water cannot be present as such in the sulphide. Moraht and Wischin suggest the following constitution:



This is supported to some extent by the facts that (1) the oxysulphide dissolves in sodium carbonate solution with evolution of carbon dioxide, and (2) yields with solid potassium sulphide a yellow substance, hydrogen sulphide escaping. These facts suggest that the oxysulphide has a distinctly acid nature. Again, with ethyl iodide, mercaptan is produced. This clearly indicates the presence of an SH group. Thus:

+ 2C₂H₅I -> + 2HI -> 2C₂H₅SH + 2OsO₂.

The precipitated osmium dioxide discloses its unsaturated nature by exploding when heated with organic substances. E. von Meyer describes the preparation of an osmium oxysulphide by passage of hydrogen sulphide through a solution of osmium tetroxide.